X-56A To Begin Active Flutter-control Tests

A testbed for future fuel-efficient transport and unmanned aircraft with slender, flexible wings has made its first flight at NASA’s Dryden Flight Research Center at Edwards AFB, Calif.

The X-56A Multi-Utility Technology Testbed (MUTT) has been built by Lockheed Martin Skunk Works for the U.S. Air Force Research Laboratory (AFRL) and NASA to test active aeroelastic control technologies for flutter suppression and gust-load alleviation.

The 28 ft.-span, 480-lb. unmanned aircraft will test to the edge of the flight envelope, where flutter occurs, to demonstrate that the potentially catastrophic aeroelastic instability can be accurately predicted and actively suppressed to enable use of lightweight, high-aspect-ratio wings to reduce drag.

If a test goes too far, and a wing fails in flight, the X-56A is fitted with a fuselage-mounted ballistic airframe-recovery parachute.

Lockheed has built two fuselages. The wings are replaceable, and the aircraft will be tested with a stiff wing as well as three sets of flexible wings.

After completing tests for AFRL, as a follow-on to its SensorCraft research program to develop technology for high-altitude, long-endurance unmanned aircraft, the X-56A will be transferred to Dryden to support work on flexible wings for future transport aircraft.

NASA is targeting a 25% reduction in wing structural weight, and a 30-40% increase in aspect ratio to reduce drag, by using active control to suppress the flutter of slender, flexible wings.

The X-56A, which is powered by two small JetCat P400 turbojects, was planned to fly last year, with the transfer to NASA then expected by the end of 2012, but encountered undisclosed delays.

During the first flight, the X-56A flew at low altitude for 14 min. while airspeed calibration data were collected and handling qualities evaluated at 70 kt., and at 60 kt. on the approach to landing.

Under the AFRL program, Lockheed is to demonstrate it can accurately predict flutter onset and actively suppress the three main aeroelastic instabilities: the rigid-body phugoid and first and second bending-torsion modes.

Flutter will be stimulated deliberately. The wing houses water ballast that will be moved in flight to change the mass distribution and mode frequencies, and prove the control system can suppress the instabilities in real time.

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